The Los Angeles basin is a Neogene rift containing a nearly ideal petroleum system. Highly organicrich strata accumulated slowly during tectonic rotation, followed by rapid subsidence and burial beneath thick successions of submarine fan deposits and nonmarine sediments. Late Miocene and Pliocene slope-channel and basin-floor fan sandstones are the main reservoirs. Most petroleum accumulations have been found in faulted anticlines that are associated with the principal structures of the basin and that have been greatly enhanced and modified by transpressional tectonics during the past 6 million years. The basin’s 68 named oil fields probably originally contained more than 40 billion barrels of oil in place. In spite of many years of production, large volumes of technically recoverable petroleum remain in undiscovered accumulations, as additional recoverable oil in existing fields, and possibly in source-rock system reservoirs. Additional large-scale development is problematic, however, owing to the complexities of oil production within a modern megacity.